Mobile communications devices incorporating global positioning system (“GPS”) capabilities are becoming popular. In these devices, the circuitry and components necessary to provide the GPS capabilities must share the same enclosure and circuit board real estate as the circuitry and components dedicated to providing, for example, mobile (cellular) telephone capabilities. Further, circuitry and components for both GPS capabilities and as mobile telephone capabilities are typically powered by the same power source, for example, via an on-board battery. While battery technology is improving, it is typical that the more power consumed by a device the larger the physical size of the battery required to provide a given operating time.
The demand for smaller, more compact mobile communication devices is increasing. Concurrent with this increasing demand for compactness is the demand for devices that provide for increased functionality and capabilities. As functionality and capabilities increase, typically, so does the need for power and printed circuit real estate within the mobile communications device.
Mobile communications devices, such as device 10 in FIG. 1, incorporate a global positioning system (GPS) receiver 100 and a communications device, such as a code division multiple access (CDMA) based communications device 200. Device 10 is a personal communications device, such as a cellular phone or any other personal mobile device with communication and GPS capabilities. In devices such as device 10 it is common for separate clock sources (oscillators) to be associated with the GPS receiver 100 and the CDMA device 200. More particularly, GPS receiver 100 includes an associated oscillator 101 while CDMA device 200 includes an associated oscillator 201. Each of the oscillators 101 and 201 provides a clock signal to the respective circuitry to which it is associated.
FIG. 2 is a block diagram of the GPS receiver 100, which includes oscillator 101. Oscillator 101 provides a signal of a particular frequency to a phase comparator 146. Phase comparator 146 also receives input from frequency divider 136 and outputs a signal to loop filter 145. Loop filter 145 provides a signal to voltage controlled oscillator (VCO) 115 which generates an output signal whose frequency is contingent upon the signal input from loop filter 145. The signal from VCO 115 is provided to mixer 110 where it is combined with a radio frequency (RF) signal from low noise amplifier (LNA) 105 to produce a first intermediate frequency (IF) signal S1. This first IF signal S1 is provided to variable amplifier 112 and then on to mixer 120 and mixer 121. In mixer 120, the signal S1 is combined with a signal S2 from frequency divider 130 to produce an in-phase second IF frequency output signal S3. In mixer 121, the signal S1 is combined with a signal S4 from frequency divider 130 to produce a quadrature-phase second IF frequency output signal S5. Signal S3 is provided to comparator and A to D processor 125 to produce a digitized signal I for output to GPS baseband section 150. Signal S5 is provided to comparator and A to D processor 126 to produce a digitized signal Q for output to GPS baseband section 150. Frequency divider 130 also provides its output signal S4 to frequency divider 135 and frequency divider 136. The output from VCO 115 is also provided to frequency divider 130. Frequency divider 130 outputs a signal S4 that is mixed by mixer 121 with a signal S1 to produce a signal S5.
As two separate oscillators are provided within the same mobile communications device 10, printed circuit board and/or integrated circuit real estate is devoted to accommodating each oscillator. Another disadvantage is that power consumption of the two oscillators is greater than for one oscillator. Thus it is desirable to have a mobile communications device that overcomes the stated disadvantages.